1. Field of The Invention
The present invention relates generally to an apparatus for controlling a damping coefficient of a shock absorber (also called a damper, but hereinafter referred to as the shock absorber) interposed between an unsprung mass and sprung mass of the vehicle so as to provide an optimum damping force therefrom. The shock absorber is provided with changing means for changing the damping coefficient thereof at multiple stages in response to a control signal.
2. Description of The Background Art
A Japanese Utility Model Registration Application First Publication No. Heisei 3-41238 published on Apr. 19, 1991 exemplifies a previously proposed apparatus for controlling a damping coefficient of the shock absorber which is provided with a variable damping coefficient.
Damping coefficient changing means of each shock absorber recited in the above-identified Japanese Utility Model Registration First Publication includes: a) a fixed orifice having a progressively incremental slit profile; and b) a variable orifice whose position can be electrically or mechanically varied, both fixed and variable orifices being arranged such as to be overlapped on two sheets of discs so that an effective orifice area is continuously varied in response to a rotation of the variable orifice.
If the damping coefficient of the shock absorber in the previously proposed controlling apparatus is in proportional control on the basis of input of sprung mass vertical speed, a target damping coefficient varying characteristic a with respect to the sprung mass vertical speed is previously set as shown in FIG. 14 and the effective orifice area is set so as to give the target damping coefficient varying characteristic a.
As shown in FIG. 15, an actual damping coefficient varying characteristic b according to a rotation position of the variable orifice described above indicates a non-linear characteristic due to complex relationships from other elements such as damping valve characteristic or constant orifice characteristic.
Therefore, a large deviation occurs between the target damping coefficient varying characteristic a denoted by a solid line of FIG. 14 and actual damping coefficient varying characteristic b denoted by a dot line of FIG. 14.